The present invention generally relates to electric power transmission devices. More particularly, the invention relates to apparatus and methods for preventing environmental contamination by dielectric insulation oil.
Electric power transmission devices such as transformers and switch gear are often immersed in a specially compounded oil with dielectric properties for purposes of insulation, isolation and cooling. On occasion, these devices generate extremely high operating temperatures. Although the oil will not burn in the absence of atmosphere or oxygen, small portions will directly decompose under the intense heat of electrical arcing into elemental carbon, which remains in the oil body as suspended graphite particles.
Additionally, the chemical nature of the oil is hydrophilic. Any atmospherically carried water coming into surface contact with the oil is adsorbed and entrained.
Both, water droplets and graphite particles are intolerable contaminants of the oil and must be removed, either periodically or continuously. Fortunately, both contaminants are effectively removed by relatively simpler depth wound unsized paper reel filters. A traditional installation often will connect a transformer oil cavity by external plumbing conduits to adjacently housed pump and filter units. Circulation around the conduit loop is driven by the pump motor which is controlled by cycle timers and filter pressure differential monitoring switches. Circulation may be continuous or intermittent, depending on the type of transformer or the service to which it is applied.
An adverse consequence of such dielectric oil is the environmentally hazardous nature of its chemical composition. Consequently, these oils are heavily regulated and monitored. Affected site clean-ups due to leaks and spills are extremely expensive and subject to the responsible manager to fines and other penalties. Accordingly, great care is exercised in handling these fluids and every reasonable precaution is taken to prevent leaks from the external filter circulation system. Nevertheless, leaks can and do occur.
It is, therefore, an object of the present invention to protect the local environment from leaks and other losses of insulating oil from transformer and other electrical power transmission devices.
Another object of the present invention is the provision of an alarm system to alert responsible management of a defective transformer oil circulation system.
A further object of the present invention is provision of a secondary conduit system enclosing the primary insulation oil circulation system for an electric power device.
These and other objects of the invention are provided by an independent insulating oil circulation system having a motor driven pump connected in fluid circuit with a filter unit. The pump, motor and filter assembly are preferably secured within an independent cabinet enclosure above a normally dry reservoir volume.
The cabinet reservoir volume is guarded by a fluid sensor such as a level switch to indicate the presence of oil within the normally dry reservoir.
Primary circulation conduits connect the filter and pump, respectively, with the oil filled cavity of an associated electric power transmission device such as a transformer, load tap changer, breaker, closure, reclosure, switch or switching bank. A full circulation loop at least includes a conduit from the transmission device oil cavity to the pump, a flow connection between the pump and the filter, a conduit between the filter and the transmission device oil cavity and an internal flow connection within the transmission device oil cavity between the pump conduit connection and the filter conduit connection.
Fluid-tight housings are secured to the external surface of the transmission device casement around respective circulation conduit connectors to or through the casement whereby the point of casement penetration by the connector is enclosed by a secondary containment volume. These housings are of such dimension and volume as to permit hand-tool accessibility through resealable port covers to the circulation conduit connectors.
The circulation conduits enter the secondary containment housing and the isolation cabinet through sealed bulkhead connectors. The bulkhead connectors are continuously interconnected by large conduits for a continuous enclosure therebetween. Accordingly, a sealed and continuous secondary fluid flow channel is established around the primary circulation system with the pump/filter cabinet reservoir, preferably at the elevationally lowest point in the system. Oil escaping from the primary circulation circuit at any point outside of the transmission device case will gravity drain to the cabinet sump volume. Depending on the type of fluid detection system used, when sufficient oil accumulates in the sump, an alarm signal is transmitted to the filter circulation and central control systems to stop the pump drive and seal off the primary circulation circuit from the oil cavity of the transmission device.